Currently, an image obtained by photographing a ground surface is mainly captured using both a camera and a sensor installed in an airplane or a satellite located at a certain altitude above the ground surface. An airplane has a relatively low altitude of several hundreds of meters to several kilometers, but has relatively unstable velocity and attitude, compared to a satellite. In contrast, a satellite is a photographing device, moving outside the atmosphere, and has a very high altitude of several hundreds of kilometers, but has relatively stable velocity and attitude, and moves along a defined elliptical orbit. Further, an aerial photograph obtained by an airplane is an image having a very high resolution, and is mainly used to produce a topographic map, an image map, digital terrain data, etc., having a small or intermediate scale. Satellites have recently become able to take high resolution images, but such images are mainly used to manufacture objects related to maps, such as a topographic map, an image map, digital terrain data, etc., having an intermediate or large scale due to their relatively low resolution. Satellites include Satellites Pour l' Observation de la Terre (SPOT), Indian Remote Sensing Satellite (IRS), Advanced Land Observing Satellite (ALOS), Land Remote-sensing Satellite (LANDSAT), and commercial earth observation satellites (IKONOS and QUICKBIRD), and have been used in various application fields, such as detection in variation related to the observation of a ground surface, or forest fire monitoring.
The image of the ground surface, taken using a photographing device, such as an airplane or a satellite, is not immediately utilized for military or industrial purposes. The reason for this is that the image of the ground surface is distorted due to the characteristics of the photographing method.
Therefore, such distortion is corrected, and a precise orthoimage, digital topographic map, three-dimensional image, etc. are produced on the basis of a corrected image and are utilized for military or industrial purposes.
In this case, the correction of distortion of an image means an operation for assigning precise and actual ground coordinates on the ground to respective coordinates on the image.
A typical method of correcting the distortion of an image (geometric correction) involves the use of a sensor model. As shown in FIG. 1, the sensor model is a formula derived from the relationship between the position of a photographing device {right arrow over (S)} and the position of a ground control point {right arrow over (P)} on the basis of the center of the earth, and is a function of image coordinates (i, j) and ground coordinates (Px, Py, Pz). In order to assign ground coordinates using a sensor model, auxiliary data, such as the position, velocity, attitude, and photographing angle of a photographing device, in addition to the image coordinates, is required. Such auxiliary data is provided by the photographing device, together with the image.
However, there is a problem in that such auxiliary data is not accurate. As shown in FIG. 2, there are errors between the photographing position (Sc) and the photographing angle of the actual photographing device, and the photographing position (S) and the photographing angle ({right arrow over (u)}) according to the auxiliary data. Further, although not shown in the drawing, there is an error between the actual attitude of the photographing device and the attitude according to auxiliary data.
As shown in FIG. 2, due to such errors, the position on the ground surface Pc actually taken by the photographing device and the position on the ground surface P obtained by the sensor model differ from each other.
Therefore, a method of revising a sensor model has been proposed to minimize errors in the ground coordinates on the ground surface caused by inaccurate auxiliary data.
Conventional methods of revising a sensor model, proposed in the prior art, performs revision so that either or both of the position and the attitude of a photographing device, according to auxiliary data, approach those of the actual photographing device.
A representative conventional method is disclosed in Korean Patent Appln. No. 10-2005-51358 entitled “method of Correcting Geometry of a Linearly Scanned Image Using Photographing Device Rotation Model”. However, currently, the relatively accurate photographing position, photographing velocity and photographing attitude of a photographing device can be detected using systems such as a Global Positioning System (GPS) or Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). That is, because of such accurate information, if a sensor model is revised by adjusting the position or attitude of a photographing device, errors in ground coordinates may be increased instead. Therefore, it is required to more easily and precisely correct the geometric distortion of an image, obtained by photographing the ground surface, by maximally utilizing such accurate information.